Printing process

ABSTRACT

A process is provided for applying printed matter to plastic substrates by coating the substrate with a composition capable of generating aluminum phosphate. A complex aluminum phosphate having at least 1 chemically-bound molecule of an hydroxy compound ROH where R is hydrogen or an organic group is preferred. The coating is heated to provide at least a partially cured layer of aluminum phosphate and the inked pattern is applied thereto.

United States Patent [191 Birchall et al.

[ Jan. 15, 1974 1 1 PRINTING PROCESS [73] Assignee: Imperial ChemicalIndustries Limited, London, England [22] Filed: 'Dec. 10, 1971 21 Appl.No.: 206,909

[30] Foreign Application Priority Data Dec. 11, 1970 Great Britain59010/70 [52] U.S. Cl ..117/15,l17/45, 117/62, 117/76 F [51] Int. ClB41m 1/24, B44d 1/32 [58] Field of Search 1l7/15,45,76 F; 423/305, 311

[56] References Cited UNITED STATES PATENTS 3,111,418 ll/l963 Gilbert117/15 3,516,842 6/1970 Klinker 117/45 2,888,406 5/1959 Bondley...252/516 2,909,451 10/1959 Lawler 423/305 FOREIGN PATENTS OR APPLICATIONS2,051,101 2/1971 France ll7/15 Primary ExaminerRalph S. KendallAssistant Examiner-M. F. Esposito Attorney-Cushman, Darby & Cushman [57]ABSTRACT A process is provided for applying printed matter to plasticsubstrates by coating the substrate with a composition capable ofgenerating aluminum phosphate. A complex aluminum phosphate having atleast 1 chemically-bound molecule of an hydroxy compound ROH where R ishydrogen or an organic group is preferred. The coating is heated toprovide at least a partially cured layer of aluminum phosphate and theinked pattern is applied thereto.

10 Claims, No Drawings PRINTING PROCESS This invention relates toorganic plastics substrates such as films or sheets, in particular to aprocess for printing the surface of such substrates, and to substratesso printed.

For many applications of plastics films, for example when a film is usedas a packaging material, it is desirable to imprint decorative ordescriptive matter on to the film surface by means of suitable inks anddyes. Hitherto, one of the problems encountered in the printing of filmsurfaces has been the difficulty of ensuring adequate adhesion of theprinted matter to the film surface to prevent peeling-off of the printedmatter during subsequent usage of the film. To improve the adhesionbetween film surface and printed matter it has been necessary to subjectthe film surface to some form of treatment which will provide a suitablebase to which the printed matter will key. Thus, the surface of apolyolefin film, for example, is etched by means of a suitable solventprior to the application of printed matter thereto. Alternatively, thefilm surface may be conditioned by treatment with an oxidising agentsuch as chromic acid or a suitably conditioned surface may be obtainedby subjecting the film surface to electron discharge treatment. Thesetreatments are difficult to apply and are economically undesirable.

We have now found that the printability of a film or sheet is improvedby providing on the surface of the film or sheet a coating of analuminium phosphate.

Accordingly, the present invention provides a process for applyingprinted matter to an organic plastics substrate comprising applying tothe substrate a coating of a composition capable of generating aluminiumphosphate on heating, heating said coating to provide a cured orpartially cured layer of aluminium phosphate and applying an inkedpattern to said cured or partially cured layer of aluminium phosphate.

Within the term substrate we include unitary films, i.e., filmsfabricated from a single component, laminated films formed by bondingtogether a plurality of film layers of the same or different chemicalcomposition, foamed films produced by incorporation of a suitableblowing'agent into the film-forming melt, and polymeric sheets. Thethickness of a film is conveniently expressed in terms of gauge, where100 gauge indicates a thickness of 0.0254 mm, and films suitable for usein the process of the present invention vary in thickness from about 25to about 1000 gauge. Substrates of thickness in excess of about 1000gauge are herein referred to as sheets.

Suitable substrates include cellulose and preferably syntheticthcrmoplastics such as polyolefins, for example polymers and copolymersof ethylene, propylene, butadiene, isoprene, 4-methyl pentene-l andstyrene, copolymers of ethylene with unsaturated esters such as vinylacetate or alkyl acrylates or methacrylates, modified polystyrene, forexample a styrene-maleic anhydride copolymer, polymers and copolymers ofother ethylenically unsaturated monomers such as vinyl chloride,vinylidene chloride, chloroprene, methyl methacrylate, ethyl acrylateand vinyl acetate, polyphenylene oxides and sulphides, polysulphones,polyoxymethylenes, polyamides such as polycaprolactam (Nylon 6),polyhexamethylene adipamide (Nylon 66) and polyundecanolactam (Nylonll), and polycarbonates and polyesters such as polyethylene lgdiphenoxyethane-4,4'-dicarboxylate and polyethylene terephthalate.

Film substrates for use in the process of the present invention areemployed in either an undrawn state, i.e., in the as cast condition, forexample films of polyvinyl chloride or polystyrene, or in a drawncondition in which the tensile properties of the film are improved bystretching the film, at a temperature above the second order transitionpoint of the polymeric film either uniaxially or biaxially in twomutually perpendicular directions in the plane of the film to orient themolecular structure of the film, and then heat setting the film at atemperature below its melting point while the film is held undertension. Typical examples of drawn film are polypropylene andpolyethylene terephthalate films.

The composition capable of generating aluminium phosphate on heating canadvantageously be a halogencontaining complex phosphate of aluminiumcontaining at least one chemically-bound molecule of a by droxy compoundR-OH wherein R is a hydrogen atom or an organic group. Such materialsare described and claimed in the complete specification of UnitedKingdom Patent Application 29862/69, which corresponds to US.application Ser. No. 42,499, now abandoned, now refiled as Ser. No.274,964, the disclosure of which is incoporated herein by reference.

On heating these complex phosphates at relatively low temperatures, ofthe order of C, to C, they decompose evolving a hydrogen halide and thecompound R-OH to form a hard abrasion-resistant aluminium phosphate. Asused herein, the term complex aluminium phosphate denotes the materialprior to decomposition by heating while the term aluminium phosphatedenotes the product obtained by decomposing the complex aluminiumphosphate by heating.

lf the complex phosphate is applied as a solution in a suitable solvent,for example water, or an alcohol such as methanol or ethanol, to asubstrate, on removing the solvent and heating to decompose the complexaluminium phosphate, the aluminium phosphate produced forms a stronglyadherent coating on the substrate that is stable to high temperatures.

l i' efei'ably the halogen in the complex aluminium phosphate ischlorine. Also it is preferred that R is an aliphatic hydrocarbon orsubstituted hydrocarbon group; in particular it is preferred that thehydroxy compound is an aliphatic alcohol containing one to four carbonatoms, particularly methanol or ehtanol, The ratio of the number of gramatoms of aluminium to the number of gram atoms of phosophorus in thecomplex phosphates of aluminium may vary over a wide range, for examplefrom 1:2 to 2:1, but is preferably substantially 1:1, as complexphosphates of the invention having this ratio decompose at lowtemperatures directly to form aluminium orthophosphate having greaterchemical stability and refractoriness than aluminium phosphate formedfrom complex phosphates with other ratios. As a typical example thecomplex aluminium phosphate has an empirical formula AlPCll-l C O whichcan be designated aluminium chlorophosphate ethanolate, although it mustbe understood that this designation in no way implies any particularmolecular structure for the compound.

In another method of preparing a suitable coating composition capable ofyielding an aluminium phosphate on heating, aluminium phosphate isdissolved or dispersed in hydrochloric, sulphuric, oxalic or citric acidor a compatible mixture of two or more such acids. Aluminiumorthophosphate, for example may be used with hydrochloric acid at molarratios varying between 1:0.1 and 1:10, preferably between 1:0.25 and1:10. Solutions obtained may optionally be diluted with water and/or analcohol, for example methanol or ethanol, before use as a coatingcomposition. It is preferred to dilute the solutions, if required,immediately before use because the dissolved phosphates are prone toprecipitate from dilute solutions on prolonged storage.

A solution of aluminium phosphate in hydrochloric acid may be for thepurposes of this invention made by dissolving aluminium chloride inphosphoric acid.

Inks for use in printing polymeric substrates are often doped withadhesion-promoting additives to improve the bond between the substrateand the inked pattern printed thereon. Thus, inks for use in theprinting of polyolefinic substrates are usually doped with polyamides asadhesion promoters. However, the process of the present inventionenables a wide range of conventional printing inks to be employed andany of the commercially available inks may be used, for example inkshaving aqueous or alcoholic or ketonic bases, or inks based onpolyacrylates or other polymeric vehicles.

The aluminium phosphate coatings of this invention are applied either toone or to both faces of the polymeric film or sheet substrate and thecoatings may be continuous, extending over the entire surface, ordiscontinuous in so far as a coating is deposited only on those portionsof the film surface to which printed matter is to be applied.

The coatings are most conveniently derived from a solution of thecomplex phosphate in aqueous or organic solvent and in the latter casewe prefer that the organic solution should be applied under essentiallyanhydrous conditions. The organic solvent is preferably a polar solvent,especially an oxygen-containing polar solvent. Especially useful arealiphatic alcohols containing up to ten carbon atoms, esters, polyhydricalcohols, and glycol esters. Most preferred are aliphatic alcoholscontaining from one to five carbon atoms, for example methanol orethanol. The solvent may be a mixture of solvents, for example amethanol/- chloroform mixture. It is especially preferred that thesolution of complex phosphate comprises a material or materials whichcontrol the physical nature of the solid phase of aluminium phosphatewhich is produced from the solution, for example by heating. When thesolvent comprises water it is preferred to use a crystallisationstabiliser, for example finely divided silica or alumina, or anucleation activator or catalyst, for example dibutyl peroxide, orcalcium, magnesium or sodium chloride. When the solution of the complexphosphate is non-aqueous, for example when the solvent is ethanol, it ispreferred to use a boric acid ester or ether or a silicic acid ester orether, for example methyl borate, trimethoxy boroxine or ethyl silicateto suppress the crystallisation of aluminium phosphate.

Application of the coating composition to the polymeric substrate isachieved by any of the conventional coating techniques, for example byspraying a solution of the coating composition on to the surface of thesubstrate or by immersing the substrate in a bath of the coatingsolution. In the case ofa film substrate, coating of both surfaces ofthe film is conveniently achieved by reeling a continuous film stripthrough a bath of the coating solution. Coating of one side of a film isreadily achieved by employment of a triple-roll system of the typeemployed in lithographic printing process. In the latter coating processfilm strip is passed through the nip between a pair of contra-rotatingcylindrical rolls, viz a coating roll and a backing roll. Coatingsolution is applied to the coating roll, and thence to a film, by meansofa transfer roll which rotates in surface contact with the coating rolland which picks up coating solution from a solution reservoir, forexample either by partial immersion of the transfer roll in thereservoir or by means of a multiple-roll train interposed between thereservoir and the transfer roll, or by any other convenient method.

As hereinbefore described, the coatings may be discontinuous, beingdeposited only on those portions of the substrate to which printedmatter is to be applied. In the case of coatings applied by a sprayingprocess, discontinuous coating is conveniently achieved by employing asuitable masking technique, whereas for coatings applied by a rollersystem a discontinuous coating is most conveniently achieved by means ofa transfer roll which is suitably profiled to deposit the desiredpattern of coating solution on to the coating roll and thence on to thefilm substrate.

The coating of phosphate solution deposited on the substrate is cured byheating, which serves both to remove solvent and to generate a stronglyadherent layer of aluminium phosphate on the substrate. Heating of thephosphate coating is effected by any convenient means, for example bypassage of the coated substrate through an air oven maintained at therequisite temperature. Alternatively, when the substrate is incapable ofwithstanding the curing temperature, the coating is heated by a methodwhich does not heat the substrate, for example by micro-wave heating.The duration of heating is preferably at least ten minutes. The form ofaluminium phosphate produced will depend, amongst other things, upon thetemperature to which the coating is heated. Although in the case of thecomplex phosphate a temperature of at least C is normally sufficient toform a coat of aluminium phosphate, the coating is preferably heated toa temperature in excess of C.

The required pattern or other printed matter is applied to the curedphosphate coating by any suitable printing technique, for example byrotary letter-press, flexographic, lithographic or photogravureprocesses.

The thickness of the cured aluminium phosphate layer is convenientlybetween about 0.1 to 20 microns, and preferably less than 10 microns,but when the coating is required to exhibit transparency we prefer tomaintain the thickness of the cured coating below about 2.5 to 3microns. Coatings of thickness greater than about 3 microns tend tobecome powdery and opaque but are preferably suitable as a base on whichto apply printed matter, provided that transparency of the coating isnot essential.

Organic materials, preferably polymers, may be dissolved in thesolutions from which the coatings of this invention are produced to givecoatings comprising an organic material and aluminium phosphate. It isadvantageous to add a suitable wetting agent, e.g. a perfluorosurfactant, to the coating solution to assist uniform coating. Othercomponents, for example pigments, may be incorporated in the coating byincluding them in the coating solution.

Although the coatings of this invention are intended for applicationdirectly on to untreated polymeric substrates, our invention does notpreclude the prior treatment of the substrate, for example by electrondischarge treatment, to promote adhesion of the coating to thesubstrate. In addition oralternatively, fillers such as finely dividedsilica, silicates or calcium carbonate may be incorporated into eitheror both the polymeric substrate and the applied coating layer to promoteadhesion therebetween.

Our invention also provides an organic plastics substrate coating with alayer of aluminium phosphate, said layer being overprinted with an inkedpattern.

If desired, the printed products of this invention may be overcoatedwith a second coating of aluminium phosphate by the techniques hereindescribed, to provide an abrasion-resistant, protective layer over theprinted matter.

The products of this invention are particularly suit able for use in thepackaging industry, for example in the packaging of foodstuffs, garmentsor other articles where a printed package is desired, and are alsosuitable for the production of decorative wall-coverings and the like.

The invention is illustrated by the following Example in which all partsand percentages are by weight:

EXAMPLE A solution was prepared by dissolving g of the aluminiumchlorophosphate ethanolate prepared as described in Example 1 in U.l(.Patent Application No. 29862/69 and 0.5 g of polyvinylpyrrolidone in 90g of methanol. This solution was used to coat polyethylene terephthalatefilm by dipping a piece of the film in a beaker of the solution andwithdrawing the film at a rate of nine inches per miniute. The dippingprocess was carried out inside a nitrogen-purged box in which therelative humidity was less than 10 percent. The solution wetted thesurface of the polyester film with a continuous layer and after dryingthe coated film at ambient temperature in the nitrogen-purged box thecoated film was removed from the box and the aluminium chlorophosphateethanolate coating containing some polyvinylpyrrolidone was cured byplacing the coated film in an oven at a temperature of 120 C for thirtyminutes. This process gave a continuous strongly adherent mixed coatingof aluminium phosphate containing 13 percent w/w polyvinylpyrrolidone onthe surface of the polyester film.

A coating of Coates Solar Red, a modified nitrocellusin wa app ie t hephq he seise s fvrtsssis of the polyester and allowed to dry. Theadhesion of the ink to the surface was tested by consecutively stickingthree strips of one-inch wide transparent adhesive tape to the printedsurface and immediately peeling the strips off keeping the tape at anangle of about l40 C to the film surface. After three pulls with freshadhesive tape only 5 percent of the ink had been pulled from thesurface.

We claim:

1. A process for applying printed matter to an or ganic plasticssubstrate comprising applying to the substrate a coating of acomposition capable of generating aluminium phosphate and containing acomplex of aluminium having at least one molecule of a hydroxy compoundROH wherein R is a hydrogen atom or an organic group, heating saidcoating to provide a cured or partially cured layer of aluminiumphosphate and applying an inked pattern to said cured or partiallycuredlayer of aluminium phosphate.

2. A process as claimed in claim 1 wherein the substrate comprisescellulose, polyolefins, copolymers of ethylene with unsaturated esters,modified polystyrene, polymers and copolymers of vinyl chloride,vinylidene chloride, chloroprene, methyl methacrylate, ethyl acrylateand vinyl acetate, polyphenylene oxides and sulphides, polysulphones,polyoxymethylenes, polyamides, polycarbonates and polyesters.

3. A process as claimed in claim 1 wherein the coating compositioncomprises a halogen-containing complex of aluminium containing at leastone chemicallybound molecule of a hydroxy compound ROI-l wherein R is ahydrogen atom or an organic group.

4. A process as claimed in claim 3 wherein the hydroxy compound is thehalogen-containing complex phosphate of aluminium is an aliphaticalcohol containing one to ten carbon atoms.

5. A process as claimed in claim 4 wherein the hydroxy compound isethanol.

6. A process as claimed in claim 3 wherein the complex phosphate ofaluminium contains chlorine.

7. A process as claimed in claim 3 wherein the complex phosphate ofaluminium has the empirical formula AIPHIHZ5CQOB.

8. A process as claimed in claim 3 wherein the coating compositioncomprises the halogen-containing complex of aluminium dissolved in anorganic solvent.

9. A process as claimed in claim 8 wherein the solvent is methanol.

10. A process as claimed in claim 3 wherein the curing of the coating iseffected at a temperature of at least C.

2. A process as claimed in claim 1 wherein the substrate comprisescellulose, polyolefins, copolymers of ethylene with unsaturated esters,modified polystyrene, polymers and copolymers of vinyl chloride,vinylidene chloride, chloroprene, methyl methacrylate, ethyl acrylateand vinyl acetate, polyphenylene oxides and sulphides, polysulphones,polyoxymethylenes, polyamides, polycarbonates and polyesters.
 3. Aprocess as claimed in claim 1 wherein the coating composition comprisesa halogen-containing complex of aluminium containing at least onechemically-bound molecule of a hydroxy compound ROH wherein R is ahydrogen atom or an organic group.
 4. A process as claimed in claim 3wherein the hydroxy compound in the halogen-containing complex phosphateof aluminium is an aliphatic alcohol containing one to ten carbon atoms.5. A process as claimed in claim 4 wherein the hydroxy compound isethanol.
 6. A process as claimed in claim 3 wherein the complexphosphate of aluminium contains chlorine.
 7. A process as claimed inclaim 3 wherein the complex phosphate of aluminium has the empiricalformula A1PC1H25C8O8.
 8. A process as claimeD in claim 3 wherein thecoating composition comprises the halogen-containing complex ofaluminium dissolved in an organic solvent.
 9. A process as claimed inclaim 8 wherein the solvent is methanol.
 10. A process as claimed inclaim 3 wherein the curing of the coating is effected at a temperatureof at least 80* C.